Reforming with multimetallic catalysts

ABSTRACT

A catalyst comprised of platinum, iridium, copper, selenium and halogen, composited with an inorganic oxide support or carrier, preferably alumina. The catalyst is one which possesses an intrinsically high activity, is stable, and can operate at reforming conditions at high severities.

RELATED APPLICATIONS

This is a division of application Ser. No. 211,765, filed Dec. 1, 1980,which is a continuation-in-part of application Ser. No. 053,375; filedJune 29, 1979, now U.S. Pat. No. 4,265,786.

BACKGROUND OF THE INVENTION AND PRIOR ART

Catalytic reforming, or hydroforming, is a process well known to thepetroleum refining industry for improving the octane quality of naphthasand straight run gasolines. In a typical process, a series of reactorsare provided with fixed beds of catalyst which receive upflow ordownflow feed, and each reactor is provided with a preheater because thereactions which take place are endothermic. A naphtha feed, withhydrogen, or recycle gas, is cocurrently passed sequentially through areheat furnace and then to the first reactor, and then again preheatedand passed to the next reactor of the series. The vapor effluent fromthe last reactor of the series is a gas rich in hydrogen, which usuallycontains small amounts of normally gaseous hydrocarbons, from whichhydrogen is separated from the C₅ ⁺ liquid product and recycled to theprocess to minimize coke production; coke invariably forming anddepositing on the catalyst during the reaction.

Reforming catalysts are recognized as dual functional, the catalystcomposite including a metal, or metals, or a compound or compoundsthereof, providing a hydrogenation-dehydrogenatin (hydrogen transfer)function and an acidic component providing an isomerization function.The platinum group metals (ruthenium, osmium, rhodium, iridium,palladium and platinum), particularly platinum, have been widely used incommercial reforming operations, these metals being composited with aninorganic oxide base, particularly alumina; and in recent yearspromoters such as iridium, rhenium, germanium, tin, etc., have beenadded, particularly to platinum, to enhance one or more of certain ofthe characteristics which a good reforming catalyst must possess-viz.,activity, selectivity, activity maintenance and yield stability.Halogen, e.g. chlorine, is generally added to provide the required acidfunction.

The principal reactions produced in reforming are dehydrogenation ofnaphthenes to produce the corresponding aromatic hydrocarbons;isomerization of n-paraffins to form branched-chain paraffins andisomerization of five membered to six membered ring compounds, anddehydrogenation of the latter to form aromatics; dehydrocyclization ofparaffins to form aromatics; and hydrocracking of high molecular weightfeed constituents to form lower molecular weight, or lower boiling,constituents, the net effect of these reactions being to increase theconcentration of aromatics and isomers, with consequent octaneimprovement of naphthas boiling within the gasoline range.Hydrogenolysis, a specific and severe form of hydrocracking, can alsooccur. This reaction, inter alia, produces excessive amounts of methaneand other hydrocarbon gases with decreased C₅ ⁺ liquid yields which canbe particularly acute with multi-metallic catalysts.

U.S. Pat. No. 2,851,399 which issued Sept. 9, 1958, to Brennan et al,discloses a reforming catalyst containing platinum and seleniumcomposited with alumina. In U.S. Pat. No. 3,884,799 to Mahoney et al,which issued May 20, 1975, there is also disclosed a catalyst andprocess for using such catalyst for reforming a petroleum hydrocarbonfraction at conventional reforming conditions, which is constituted of aGroup VIII noble metal, notably platinum, and rhenium and seleniumcomposited on a refractory inorganic oxide, notably alumina, to which isadded a halogen component, notably a chloride. This reference discussesthe problem of hydrogenolysis which occurs in reforming during start-upwith an unsulfided, or improperly sulfided, halogenated platinum-rheniumcatalyst; and it discloses and claims the process of using a reformingcatalyst in which selenium is incorporated therein thereby reducing cokeformation and eliminating any necessity of a pre-sulfiding treatment ofthat particular catalyst to suppress hydrogenolysis during start-up.

In U.S. Pat. No. 4,151,115 which issued Apr. 24, 1979, to Paul E.Eberly, Jr., there is disclosed a reforming catalyst comprised ofalumina and a Group VIII noble metal hydrogenation-dehydrogenationcomponent, notably platinum, to which both iridium and selenium havebeen added to promote the activity and selectivity of the catalyst. Thecatalyst is prepared by a method wherein the selenium is introduced intoand deposited throughout the support, and suitably the reformingcatalyst contains a halogen component, particularly chlorine; andpreferably the selenium component is introduced into the support, orcatalyst, by impregnating same with a solution comprising selenium as anelement, or a salt or compound thereof.

In copending application Ser. Nos. 029,675 and 034,596, filed Apr. 13,1979 and Apr. 30, 1979, respectively, and now U.S. Pat. No. 4,251,391and U.S. Pat. No. 4,251,392, respectively, there are also disclosedcatalysts and methods for the preparation of catalyst compositionscomprised of platinum or platinum and palladium, rhenium, halogen, andpreferably sulfur, composited with an inorganic oxide support, orcarrier, to which a small concentration of copper is added to improvethe yield and stability of the catalyst in reforming. And, in Ser. No.053,375, supra, there is disclosed platinum-selenium catalysts to whicha small amount of copper has been added. Copper is an essentialcomponent of such compositions; it having been found, inter alia, thatexcessive C₂ ⁺ hydrocarbon gas formation could be suppressed by the useof small and critical concentrations of copper, and that added benefitscould be obtained by the further addition of sulfur to the catalyst tosuppress hydrogenolysis.

It is nonetheless an objective of the present invention to provide a newand improved catalyst, and process for utilizing such catalyst toupgrade naphthas by reforming to produce higher octane gasolines.

A particular object is to provide a highly active catalyst, and processfor effecting, at suitable reforming conditions, the production of highoctane gasolines while minimizing hydrogenolysis and other types ofhydrocracking which tend to produce methane and hydrocarbon gases ofhigher molecular weight than methane.

Another object is to provide a catalyst which is capable of reformingfeed of high sulfur level; the catalyst being particularly resistant tosulfur poisoning.

These and other objects are achieved in accordance with the presentinvention embodying a catalyst comprised of platinum, iridium, copper,selenium, and halogen composited with an inorganic oxide support, orcarrier, preferably alumina. The catalyst possesses an intrinsicallyhigh activity, and provides good yield and stability in reforming. Thecatalyst may also contain a sulfur component.

The catalyst is one which contains platinum as an essential component,generally in concentration ranging from about 0.1 percent to about 2percent, preferably from about 0.2 percent to about 0.6 percent, basedon the weight of the catalyst (dry basis).

The catalyst also contains iridium as an essential component, generallyin concentration ranging from about 0.1 percent to about 2 percent,preferably from about 0.2 to about 0.6 percent, based on the weight ofthe catalyst (dry basis).

The catalyst also contains copper as an essential component, generallyin concentration ranging from about 0.01 percent to about 0.1 percent,preferably from about 0.025 percent to about 0.08 percent, based on theweight of the catalyst (dry basis). Preferably, the copper is compositedwith the catalyst in amount sufficient to provide an atom ratio ofcopper:(platinum plus iridium) ranging from about 0.008:1 to about1.54:1, preferably from about 0.12:1 to about 0.61:1. The coppercomponent is conveniently added to the catalyst by impregnation. It isimportant that the concentration of copper on the catalyst be controlledto the proper level because high concentrations of copper act as apoison and depresses catalyst activity.

Selenium is contained within the catalyst as an essential component,suitably in concentration ranging from about 0.001 to about 3 percent,preferably from about 0.01 to about 1 percent, based on the weight ofthe catalyst (dry basis). The selenium is incorporated into the catalystat the time of its formation, preferably by impregnation of a solutionof a soluble salt, acid or compound of selenium into the carrier. Theselenium incorporation step can be carried out simultaneously with,prior to, or following the impregnation of thehydrogenation-dehydrogenation component, or other components, into thecarrier. Selenium, in accordance with this invention, can be added tothe carrier from a solution which contains both the salt, acid, orcompound of selenium, the hydrogenation-dehydrogenation component, orother components, and the inorganic acid such as HCl. Suitably, thesalts or compounds are dissolved in a suitable solvent, preferablywater, to form a solution, or each moiety is separately dissolved in asolution, the solutions admixed and the admixed solution used forimpregnation of the carrier. The concentration of the salt or compoundof selenium in the impregnation solution ranges from about 0.01 to 2percent, preferably from about 0.01 to 1 weight percent, based on theweight of the solvent; this concentration being adequate to impregnate asufficient amount of the selenium within the catalyst.

Halogen is an essential component, the halogen content of the catalystgenerally ranging from about 0.1 to about 2.5 percent, preferably fromabout 0.7 to about 1.2 percent, based on the weight of the catalyst (drybasis).

Sulfur is a preferred, but not an essential component. The sulfurcontent of the catalyst generally ranges to about 0.2 percent,preferably from about 0.01 percent to about 0.1 percent, based on theweight of the catalyst (dry basis). The sulfur can be added to thecatalyst by conventional methods, suitably by breakthrough sulfiding ofa bed of the catalyst with a sulfur-containing gaseous stream, e.g.,hydrogen sulfide in hydrogen, performed at temperatures of from about350° F. to about 1050° F., and at pressures of from about 1 to about 40atmospheres for the time necessary to achieve sulfur breakthrough, orthe desired sulfur level.

The several components of the catalyst are composited with a refractoryinorganic oxide support material, particularly alumina. Suitably, thecopper is added first to the support, and subsequently the othercomponents are added. The halogen component, particularly chlorine, isadded along with the various components, or subsequent thereto, or both.The support can contain, for example, one or more of alumina, bentonite,clay, diatomaceous earth, zeolite, silica, activated carbon, magnesia,zirconia, thoria, and the like; though the most preferred support isalumina to which, if desired, can be added a suitable amount of otherrefractory carrier materials such as silica, zirconia, magnesia,titania, etc., usually in a range of about 1 to 20 percent, based on theweight of the support. A preferred support for the practice of thepresent invention is one having a surface area of more than 50 m² /g,preferably from about 100 to about 300 m² /g, a bulk density of about0.3 to 1.0 g/ml, preferably about 0.4 to 0.8 g/ml, an average porevolume of about 0.2 to 1.1 ml/g, preferably about 0.3 to 0.8 ml/g, andan average pore diameter of about 30 to 300 A.

The metal components can be composited or intimately associated with theporous inorganic oxide support or carrier by various techniques known tothe art such as ion-exchange, coprecipitation with the alumina in thesol or gel form, and the like. For example, the catalyst composite canbe formed by adding together suitable reagents such as a salt of therequired metals and ammonium hydroxide or ammonium carbonate, and a saltof aluminum such as aluminum chloride or aluminum sulfate to formaluminum hydroxide. The aluminum hydroxide containing the salts can thenbe heated, dried, formed into pellets or extruded, and then calcined inair or other atmosphere. The metal hydrogenation-dehydrogenationcomponents are preferably added to the catalyst by impregnation,typically via an "incipient wetness" technique which requires a minimumof solution so that the total solution is absorbed, initially or aftersome evaporation.

Suitably, the copper, and other metal components, is deposited on apreviously pilled, pelleted, beaded, extruded, or sieved particulatesupport material by the impregnation method. Pursuant to theimpregnation method, porous refractory inorganic oxides in dry orsolvated state are contacted, either alone or admixed, or otherwiseincorporated with a metal or metals-containing solution, or solutions,and thereby impregnated by either the "incipient wetness" technique, ora technique embodying absorption from a dilute or concentrated solution,or solutions, with subsequent filtration or evaporation to effect totaluptake of the metallic components.

In compositing the metals with the carrier, essentially any solublecompound of the respective metal can be used, but a soluble compoundwhich can be easily subjected to thermal decomposition and reduction ispreferred; for example, inorganic salts such as halides, nitrates,inorganic complex compounds, or organic salts such as the complex saltof acetylacetone, amine salt, and the like. In adding the copper, copperchlorides and nitrates are preferred sources of copper on the basis ofavailability, cost and effectiveness.

The copper is incorporated into the catalyst at the time of itsformation, or thereafter, and preferably the copper is incorporated intothe pre-formed carrier by impregnation from a solution of a solublesalt, or compound of copper; preferably in a solution of hydrochloricacid to provide good distribution of the copper. This step is carriedout prior to the impregnation of the hydrogenation-dehydrogenationcomponents. The copper, in accordance with this invention, can be addedto the carrier from a solution which contains a salt, or compound ofcopper, and thereafter the copper impregnated support can be dried,calcined, and the hydrogenation-dehydrogenation components then added,suitably as salts or compounds dissolved in a suitable solvent,preferably water, to form a solution.

The impregnation of the platinum component, and other components, into acarrier is carried out by impregnating the carrier with a solution, orsolutions, of the respective salts or compounds of the elements ormetals to be incorporated. Salts, acids or compounds of each metal canbe dissolved in a solution, or the salts, acids or compounds can beseparately dissolved in solutions, the solutions admixed, and thesolution used for impregnation of the carrier. In other words, copper isadded initially using conventional techniques, and then the other metalsare added simultaneously or sequentially, suitably by impregnation. Theamount of impregnation solution used should be sufficient to completelyimmerse the carrier, usually within the range from about 1 to 20 timesof the carrier by volume, depending on the metal concentration in theimpregnation solution. The impregnation treatment can be carried outunder a wide range of conditions including ambient or elevatedtemperatures and atmospheric or supratmospheric pressures.

In a preferred embodiment of the present invention a carrier isimpregnated with an aqueous halogen-acid solution of the copper.Exposure to a halogen acid can introduce substantially high levels ofhalogen into the carrier which is not desirable because subsequent metalimpregnation is inhibited and the catalyst can produce high acidcracking in reforming. However, excess halogen can be readily removedfrom the acid treated carrier by neutralization with ammonium hydroxide,suitably by contact at ambient temperature for periods ranging fromabout 0.1 to about 1 hour, at strengths ranging from about 0.1 N toabout 15 N, preferably from about 0.1 N to about 5 N. These treatmentsare followed by evaporation or filtration and then drying orcalcination, or both, and then the metals impregnated catalyst can befurther impregnated with a solution containing (1) a dissolved salt orcompound of platinum, or platinum and additional metals, (2) a dissolvedsalt or compound of iridium, (3) a dissolved salt or compound ofselenium, and (4) hydrochloric acid, followed by evaporation orfiltration, with subsequent drying or calcination, or both, whereby thecomponents are dispersed substantially uniformly to the inner part ofthe catalyst.

As suggested, a halogen component is also required. Fluorine andchlorine are preferred halogen components. The halogen is contained onthe catalyst in concentration ranging from about 0.1 percent up to about2.5 percent, preferably within the range of about 0.7 to about 1.2percent, based on the weight of the catalyst. The introduction ofhalogen into catalyst can be carried out by any method and at any timeof the catalyst preparation; for example, prior to, following orsimultaneously with the impregnation of the platinum, iridium, copperand selenium components. In the usual operation, the halogen componentis introduced simultaneously with the incorporation of these metalcomponents. It can also be introduced by contacting a carrier materialin a vapor phase or liquid phase with a halogen compound such ashydrogen fluoride, hydrogen chloride, ammonium chloride, or the like.

The catalyst, after impregnation, is dried by heating at a temperatureabove about 80° F., preferably between about 150° F. and 300° F., in thepresence of nitrogen or oxygen, or both, in an air stream or undervacuum. The catalyst is calcined at a temperature between about 500° F.,preferably about 500° F. to 850° F., in the presence of oxygen in an airstream or in the presence of an inert gas such as N₂ or in the presenceof a mixture of O₂ and inert gas. This calcination or activation isconducted for periods ranging from about 1 to about 24 hours in eitherflowing or static gases. Reduction is performed by contact with flowinghydrogen at temperatures ranging from about 350° F. to about 1050° F.for periods ranging from about 0.5 to about 24 hours at about 1-40 atm.The catalyst can be sulfided by use of a blend of H₂ S/H₂ and performedat a temperature ranging from about 350° F. to about 1050° F. at about1-40 atm. for a time necessary to achieve breakthrough, or the desiredsulfur level. Post-sulfiding stripping can be employed if desired atconditions similar to those for reduction of the catalyst.

Treatment of the catalyst with a mixture of chlorine and oxygen can besubstituted for air activation if desired. This procedure can correctfor any possible maldistribution of the metals arising from improperimpregnation, and the procedure is useful in restoring activity duringregeneration-rejuvenation after on oil service. A blend of chlorine,oxygen, and nitrogen can also be employed at temperatures ranging fromabout 350° F. to about 1050° F. for periods ranging from about 1 toabout 24 hours at 1-40 atm. Treat times for these various operations area function of gas flow rates, gas compositions, and conditions. Thecatalyst halide content can be controlled during impregnation, oradjusted by treatment with water or water-hydrogen chloride blends.

This catalyst can be used in semi-regenerative, cyclic, semicyclic, orcontinuous bed reforming. It is particularly useful in cyclic reformingoperations. The catalyst is particularly useful at severe reformingconditions, especially at low pressures, or pressures ranging from about50 psig to about 150 psig, where maximum yield is favored.

The feed or charge stock can be a virgin naphtha, cracked naphtha, aFischer-Tropsch naphtha, or the like. Typical feeds are thosehydrocarbons containing from about 5 to 12 carbon atoms, or morepreferably from about 6 to about 9 carbon atoms. Naphthas, or petroleumfractions boiling within the range of from about 80° F. to about 450°F., and preferably from about 125° F. to about 375° F., containhydrocarbons of carbon numbers within these ranges. Typical fractionsthus usually contain from about 20 to about 80 vol. % paraffins, bothnormal and branched, which fall in the range of about C₅ to C₁₂, fromabout 10 to 80 vol. % of naphthenes falling within the range of fromabout C₆ to C₁₂, and from 5 through 20 vol. % of the desirable aromaticsfalling within the range of from about C₆ to C₁₂.

The reforming runs are initiated by adjusting the hydrogen and feedrates, and the temperature and pressure to operating conditions. The runis continued at optimum reforming conditions by adjustment of the majorprocess variables, within the ranges described below:

    ______________________________________                                        Major Operating Typical Process                                                                           Preferred Process                                 Variables       Conditions  Conditions                                        ______________________________________                                        Pressure, Psig  50-750      100-300                                           Reactor Temperature, °F.                                                               750-1100     850-1000                                         Gas Rate, SCF/B  1500-10,000                                                                              2000-7000                                         (Incl. Recycle Gas)                                                           Feed Rate, W/Hr/W                                                                             0.5-10      1-3                                               ______________________________________                                    

The invention will be more fully understood by reference to thefollowing demonstrations and examples which present comparative dataillustrating its more salient features. All parts are given in terms ofweight except as otherwise specified.

EXAMPLES

A series of catalysts (Catalyst A through E) were prepared from portionsof 1/16" high purity gamma alumina extrudates by calcining same in airat 1000° F. for 4 hours. Where copper was added, the extrudates wereimpregnated overnight with a stock solution of cuprous chloride in 1 Nhydrochloric acid. The extrudates were washed with water and soaked inammonium hydroxide solution for 1 hour to remove excess chloride. Afterwashing with water the extrudates were impregnated with an aqueoussolution of chloroplatinic acid, perrhenic acid, or selenous acid, oradmixture thereof, as required, and hydrochloric acid using CO₂ as animpregnation aid. The catalysts were air-dried and then dried in vacuumat 130° F. overnight. The catalysts were air activated and reduced. Thecomposition of the catalysts are given in Table I.

                  TABLE I                                                         ______________________________________                                                 Catalysts                                                            Components A        B      C      D    E                                      ______________________________________                                        Platinum   0.3      0.3    0.3    0.3  0.3                                    Iridium    0.3      0.3    0.3    0.3  0.3                                    Selenium   0        0.04   0      0.04 0.04                                   Copper     0        0      0.05   0.05 0.25                                   Chloride   0.9      0.9    0.9    0.9  0.9                                    Alumina    98.50    98.46  98.45  98.41                                                                              98.21                                  ______________________________________                                    

The catalysts were each then contacted at reforming conditions inseparate runs with n-heptane with the results given in Table II.

                  TABLE II                                                        ______________________________________                                                Yield, Wt. %                                                          Catalyst  C.sub.5 -   Benzene  Toluene                                        ______________________________________                                        A         19.8        7.0      38.5                                           B         12.2        3.9      41.0                                           C         13.8        4.4      42.2                                           D         10.5        2.6      46.0                                           E         10.9        1.2      38.6                                           ______________________________________                                    

From these data it is shown that Catalyst D, the catalyst of thisinvention, provides lower gas make with concurrent higher activity andselectivity to aromatics than produced by any of Catalysts A, B, C, orE. Catalyst E, a catalyst which also contains all of Pt, Ir, Se and Cu,is woefully inadequate even as contrasted with Catalysts A, B and C. Thehigh copper content thus drastically reduces the activity andselectivity of the catalyst, this catalyst producing far less totalaromatics than any of Catalysts A through D.

It is apparent that various modifications and changes can be madewithout departing from the spirit and scope of the present invention,the outstanding features of which are that hydrogenolysis can besuppressed and the yield and activity maintenance can be improved evenat high severity conditions.

Having described the invention, what is claimed is:
 1. A process forreforming a hydrocarbon feed at reforming conditions which comprisescontacting said feed with a catalyst which comprises from about 0.1 toabout 2 percent platinum, from about 0.1 to about 2 percent iridium,from about 0.01 to about 0.1 percent copper, from about 0.001 to about 3percent selenium, and from about 0.1 to about 2.5 percent halogen,composited with an inorganic oxide support.
 2. The process of claim 1wherein the catalyst contains from about 0.2 to about 0.6 percentplatinum.
 3. The process of claim 1 wherein the catalyst contains fromabout 0.2 to about 0.6 percent iridium.
 4. The process of claim 1wherein catalyst contains from about 0.025 to about 0.08 percent copper.5. The process of claim 1 wherein the catalyst contains from about 0.01to about 1 percent selenium.
 6. The process of claim 1 wherein thecatalyst contains from about 0.2 to about 0.6 percent platinum, fromabout 0.2 to about 0.6 percent iridium, from about 0.025 to about 0.08percent copper, from about 0.01 to about 1 percent selenium, and whereinthe copper is composited with the catalyst in amount sufficient toprovide an atom ratio of copper:platinum ranging from about 0.008:1 toabout 1.54:1.
 7. The process of claim 6 wherein the catalyst containsfrom about 0.7 to about 1.2 percent halogen.
 8. The process of claim 1wherein the catalyst is sulfided, and contains to about 0.2 percentsulfur.
 9. The process of claim 8 wherein the catalyst contains fromabout 0.05 to about 0.1 percent sulfur.